1. Field of the Invention
This invention relates to an apparatus and method for metered feeding of plastic particulates from a feed hopper to the feed pocket of a plasticating screw.
2. Description of the Prior Art
A plasticating extruder or injection machine comprises a rotating screw within a cylinder which receives polymer pellets or powder, heats and works the polymer sufficiently to convert it to a melted or plastic state and delivers the melted polymer through a restricted outlet or die.
The cylinder for the plasticating screw is provided with a feed opening for receiving plastic pellets from an overhead hopper. The pellets commonly flow from the overhead hopper through a feed throat conduit to the feed opening on the cylinder with some type of flow regulating means disposed within the feed throat conduit.
The prior art flow regulating devices commonly entailed flood feeding wherein a considerable reservoir of feed particulates could accumulate below the flow regulating valve and above the rotating screw. Thereby, a flood feeding device commonly oversupplied the flight root of the screw with particulates. The oversupply of particulates created two problems. First, the escape passage back to the feed conduit of water vapor and resin volatiles formed within the screw could become blocked by a static oversupply of feed particulates in the feed throat. Secondly, and more importantly, the flood of feed particulates above the feed opening of the cylinder created a high shear drag between the rotating screw and its surrounding cylinder as the screw rotated. High shear forces increase the energy requirements of the plasticating device.